1. Field of the Invention
The present invention relates generally to a Main Steam Line Plug (MSLP) and more specifically to an improved Main Steam Line Plug (MSLP) which features a lock and seal arrangement which provides a seal which facilitates Local Leak Rate Tests (LLRT), and a positive locking engagement which prevents accidental ejection of the plug into the vessel.
2. Description of the Related Art
The purpose of the Main Steam Line Plug (MSLP) is to seal the main steam lines in reactors such as Boiling Water Reactors (BWR) during outages. The plug seals against the static water head present whenever the reactor cavity is flooded. In addition, the plug seals against pressure downstream in the line during Local Leak Rate Test (LLRT) while providing a positive locking force to prevent accidental ejection of the plug into the vessel.
There are three basic problem areas associated with the MSLP's currently in use. The first is the difficulty in activating the seals which prevent leakage from the static head. After initial installation, which is performed individually with each plug, the seals must be mechanically engaged. This, of course, is a labor intensive and time consuming process.
Secondly, some current plugs have no means via which they can be fixed in place in the steam lines. This induces the drawback that they are incapable of withstanding the LLRT back pressure, thereby necessitating that the LLRT is testing performed on the downstream side of the valve to be tested instead of the preferred upstream side.
Thirdly, the current plugs are often difficult to remove. This is due to the mechanical seals sticking fast in the steam lines and the inability of the steam line to be back filled prior to removal of the plug. To overcome this sticking problem it is not uncommon for the steam line to require pressurization in order that stubborn plugs be forced out.